A Study of LY3541860 in Adult Participants With Moderately to Severely Active Rheumatoid Arthritis

The main purpose of this study is to evaluate the effects of LY3541860 in adult participants with moderately to severely active Rheumatoid Arthritis with inadequate response to a least one biologic disease-modifying antirheumatic drug (bDMARD)or targeted synthetic disease-modifying antirheumatic drug (tsDMARD). Study participation is approximately 50 weeks, including a 6-week screening period, 24-week treatment period, and a 20-week safety follow up period.

Inclusion Criteria: * Have a diagnosis of adult-onset Rheumatoid Arthritis (RA) for at least 3 months prior to screening, as defined by the 2010 ACR/EULAR classification criteria. * Have moderately to severely active RA, at screening (Visit 1) and baseline (Visit 2), defined by the presence of * ≥6 swollen joints based on 66 joint count (and ≥4 swollen joints on 28 joint count), and * ≥6 tender joints based on 68 joint count (and ≥4 tender joints on 28 joint count). * Have active synovitis in ≥1 joint, in hands or wrists, of the investigator choosing at screening, having an MRI synovitis RAMRIS score of ≥2 as determined from the central reading of the images. Exclusion Criteria: * Have a diagnosis or history of malignant disease within 5 years prior to baseline, with the exceptions of * basal cell or squamous epithelial carcinomas of the skin that have been resected with no evidence of metastatic disease for 3 years, or * cervical carcinoma in situ, with no evidence of recurrence within the 5 years prior to baseline. * Have estimated glomerular filtration rate (eGFR) of \